This invention relates to internal combustion engines, both spark ignition (SI) internal combustion (IC) engines, and compression ignition (CI) internal combustion engines such as diesel engines. It also relates to the coating of the internal surfaces of internal combustion engines, in particular, it relates to the coating of the unwiped surface of a combustion chamber exposed to combustion gases, the intake valves, the surface of the intake manifold exposed to fuel-air mixtures, and the surface of the exhaust manifold exposed to exhaust gases.
It has been recognized that the thermal efficiency of the internal combustion engine could be improved by coating the aforementioned combustion chamber surfaces with a thermally insulating coating to reduce heat losses to the coolant during the compression and power cycles (fully 30-40% of the total heat generated in an IC engine is lost to the coolant). U.S. Pat. Nos. 4,074,671 and 3,820,523 provide a thin ceramic coating of the combustion chamber surface for this purpose. U.S. Pat. Nos. 3,911,891 and 3,552,370 provide for the deposition of layers of certain materials for the same purpose.
U.S. Pat. Nos. 3,066,663 and 3,019,277 teach the coating of certain combustion chamber surfaces with a ceramic insulation of appropriate thickness and thermal conductivity purportedly to avoid the formation of surface-ignition and rumble-causing deposits when a fuel or lubricant containing phosphorous is used in a high compression engine.
The deposition of substances on combustion chamber surfaces is believed to lead to an increase in the octane requirement of new spark ignited engines as they operate on unleaded fuels due to increased compression ratio and heat regenerated to the fresh air-fuel charge. Octane requirement increase, ORI, in such a case can be as much as six or more octane numbers. The "octane requirement" is the minimum octane necessary to avoid noticeable knock. Avoidance of ORI would permit the use of higher compression ratios for greater efficiency and/or the use of lower octane unleaded fuel.
A thermal insulating coating on the piston top surface would also tend to reduce the heat loading of the piston. This in turn would reduce the rate of deposit formation in the ring belt zone thereby reducing ringsticking.
Insulated intake manifolds and intake valves decrease heating of the intake air-fuel charge in SI engines, which reduces their octane requirement, and decreases intake air heating in CI engines, which improves their volumetric efficiency.
Insulated exhaust manifolds increase the heat available to turbo-charge CI and SI engines and increase the temperature of exhaust gases at the catalyst in SI engines.
A low heat capacity, insulating coating on the piston top surface and combustion chamber surfaces reduces the thickness of the non-burning quench layer near these surfaces and improves volatilization during combustion of any hydrocarbon liquids which are on the surfaces. These two processes promote hydrocarbon burning and reduce hydrocarbon exhaust emissions.